Major information about volcanoes
The study of volcanoes is called volcanology and it describes all of the processes connected with forcing solid, liquid and gaseous material onto the earth surface or into its crust. Before this material is pushed up it is kept in a semi-solid state on the top of the mantle. As processes of folding or other movements occur, pressure is released and semi-solid state is changed to molten. Next, convection currents in the mantle and pressure released result in rising of magma, which fills the cracks of the crust. When lava reaches the surface it rapidly cools and solidifies.
Summarizing, volcano is an opening in the Earth’s surface through which lava, associated gasses and ash erupt. The word volcano also refers to a conical shape made by erupting material. Volcanoes are commonly found near plate tectonic boundaries, mainly on the Pacific Ring of Fire (Pacific basin).
Volcanoes have a long, long history reaching the times and decades far before humans existed. Many scientists think that when the continents were formed the Earth had undergone many severe volcanic eruptions. The word volcano comes from Vulcan, Romanian god of fire and metal, praised as the father of all eruptions.
As most remarkable eruptions in mankind history we can consider: eruption of Mount Vesuvius in 79 A.D. (destroyed the city of Pompei - covered with ash), 1883 explosion of Krakatoa ( 36,000 people died on islands Sumatra and Java under tidal wave caused by the eruption) and not so long ago eruption of St.Helen in 1980 ( the total of 66 people died).